Water entry of cups and disks

Jesse Belden, Nathan Bevan Speirs, Aren M. Hellum, Matthew Jones, Anthony J. Paolero, T. T. Truscott

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


It is known that the water entry of a body with a recessed, cupped nose can suppress the splash and air cavity typically observed for solid body entry (Mathai, Govardhan & Arakeri, Appl. Phys. Lett., vol. 106, 2015, 064101). However, the interplay between the captive gas in the cup, the cavity and the splash is quite subtle and has not been thoroughly explored. Here we study the cavity and splash dynamics associated with the vertical water entry of cups and find a variety of regimes over a range of Weber numbers ( WeD) and dimensionless cup depths. Our parameter space spans a transition between slow-developing cavities with long closure times (low WeD) to fast-sealing cavities (high WeD). An important dynamic event is the evacuation of trapped gas from within the cup, which drives the ensuing cavity and splash behaviour. Through modelling, we predict the conditions for which the evacuating gas inflates a cavity that opens to the atmosphere versus inflating a submerged cavity that suppresses air entrainment from above the surface. We also compare our cup water entry findings to the impact phenomena observed for flat disks, which entrap gas on the front surface similar to cups. In doing so, we reveal the sensitivity of disk splash and cavity behaviour to impact angle, and show that disks share a common regime with cups, in which a thin splash quickly seals on the body. We deduce the mechanisms by which increasing cup depth delays the cavity seal time in this regime. These findings reveal that cups may in fact promote or suppress cavity growth, depending on the cup depth and impact conditions.
Original languageEnglish (US)
JournalJournal of Fluid Mechanics
StatePublished - May 16 2023

Bibliographical note

KAUST Repository Item: Exported on 2023-05-19
Acknowledgements: J.B., N.B.S, A.J.P. and A.M.H. acknowledge funding from the Naval Undersea Warfare Center In-House Laboratory Independent Research program, monitored by Dr. Tony Ruffa. M.J. and T.T.T. acknowledge funding from the Office of Naval Research, Navy Undersea Research Program (grant N0001414WX00811), monitored by Ms. Maria Medeiros. We thank Heather Kane for help in data processing.

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Condensed Matter Physics


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